import u3
from time import sleep

def noiselevel( a ):
    mean = sum(a) / len(a)
    sdiff = 0
    for e in a:
        sdiff += (e-mean)**2
    return ((sdiff/(len(a)-1))**0.5)

d = u3.U3()
d.configU3()
d.configIO( FIOAnalog = 1 )
d.streamConfig( NumChannels = 1, PChannels = [ 0], NChannels = [ 31 ], 
Resolution = 3, SampleFrequency = 5000 )

def measure():
    try:
        d.streamStart()
        
        for r in d.streamData():
            if r is not None:
                if r['errors'] or r['numPackets'] != d.packetsPerRequest or r['missed']:
                    print "error"
                else:
                    res = noiselevel( r['AIN0'] )
                break
    finally:
        d.streamStop()
    return r

def writeData( r ):
    f = open( 'noise.txt', 'w' )
    ch0 = r['AIN0']
    for i in range(0, len(ch0)-1):
        f.write( '{0:.6f}\n'.format(ch0[i]) )
    f.close()

def setVoltage():
    f = open( 'setVolts.txt', 'r' )
    V = float(f.read())
    d.writeRegister(5000,V) #writes the voltage found in setVolts.txt to DAC_0
    
for i in range(1,1000):
    writeData( measure() )
    sleep(1)
    setVoltage()